Mesothelin is a glycosyl-phosphatidylinositol anchored glycoprotein present on the cell surface of various human solid tumors. Mesothelin was first identified with the monoclonal antibody (mAb)K1 (Chang et al., Cancer Research 52: 181-186, 1992). The Mesothelin (MSLN) gene encodes a 71-kDa precursor protein that is processed to a 40-kDa glycosyl-phosphatidylinositol anchored protein, the mature portion to which mAB K1 binds, termed Mesothelin, and a NH2-terminal 31-kDa fragment called megakaryocyte-potentiating factor that is released from the cell. Mesothelin is a tumor differentiation antigen present at low levels on a restricted set of normal adult tissues, such as mesothelium, but aberrantly overexpressed in mesotheliomas, ovarian and pancreatic cancers (Hassan et al., Clinical Cancer Research 10: 3937-3942, 2004). Thus, MSLN is a promising candidate for the development of cancer vaccines.
Mesothelin (MSLN) has been described as a target antigen for immunotherapy (Hassan et al., Clin Cancer Res, 10: 3937-3942, 2004). Several immunotherapeutic approaches have been used to target MSLN overexpressing tumor types. Hassan et al. (Clin Cancer Res, 10: 3937-39422004) discloses anti-mesothelin immunotoxin SS1P [SS1(dsFv)PE38] exhibiting antitumor activity in adult nude mice. In recent years, several early phase clinical trials based on the administration of anti-mesothelin immunotoxin SS1P or chimeric anti-mesothelin monoclonal antibody MORAb-009 via bolus injection or continuous intravenous infusion have been started (comprehensively summarized in Kelly et al., Mol Cancer Ther., 11(3):517-525, 2012). Another immunotherapeutic approach currently tested in phase VII clinical trials is based on the administration of anti-mesothelin modified lymphocytes (ClinicalTrials.gov; Identifyers NCT01355965 and NCT01439152). Dung et al. (Clin Cancer Res, 18(3):858-868, 2012) discloses a Listeria monocytogenes based mesothelin vaccine, which is administered intravenously. Yamasaki et al. (Int J Cancer, 133(1): 1-17, 2013) discloses and intravenous genetic Mesothelin vaccine based on human adenovirus 40.
Attenuated derivatives of Salmonella enterica are attractive vehicles for the delivery of heterologous antigens to the mammalian immune system, since S. enterica strains can potentially be delivered via mucosal routes of immunization, i.e. orally or nasally, which offers advantages of simplicity and safety compared to parenteral administration. Furthermore, Salmonella strains elicit strong humoral and cellular immune responses at the level of both systemic and mucosal compartments. Batch preparation costs are relatively low and formulations of live bacterial vaccines are highly stable. Attenuation can be accomplished by deletion of various genes, including virulence, regulatory, and metabolic genes.
Several Salmonella typhimurium strains attenuated by aro mutations have been shown to be safe and effective delivery vehicles for heterologous antigens in animal models.
Approaches of delivering DNA constructs encoding antigens, in particular the tumor stroma antigen VEGFR, via live attenuated Salmonella typhimurium strains into mouse target cells are described in WO 03/073995. Niethammer et al., (Nature Medicine 2002, 8(12), 1369) demonstrated that the attenuated S. typhimurium aroA strain SL7207 harboring an expression vector encoding the murine vascular endothelial growth factor receptor 2 (VEGFR-2 or FLK-1), which is essential for tumor angiogenesis, is functional as a cancer vaccine.
There is however only one attenuated Salmonella enterica serovar strain, namely Salmonella enterica serovar typhi Ty21a (short: S. typhi Ty21a), which has been accepted for use in humans and is distributed under the trade name of Vivotif® (Berna Biotech Ltd., a Crucell Company, Switzerland; marketing authorization number PL 15747/0001 dated 16 Dec. 1996).
This well-tolerated, live oral vaccine against typhoid fever was derived by chemical mutagenesis of the wild-type virulent bacterial isolate S. typhi Ty2 and harbors a loss-of-function mutation in the galE gene, as well as other less defined mutations. It has been licensed as typhoid vaccine in many countries after it was shown to be efficacious and safe in field trials.
WO 2013/091898 discloses a method for growing attenuated mutant Salmonella typhi strains lacking galactose epimerase activity and harboring a recombinant DNA molecule.
MSLN is a promising tumor antigen for the development of cancer vaccines. Major limitations of previously available MSLN vaccines are the administration via the intravenous route of administration and the associated side effects. The great need for improved cancer therapy approaches based on targeting MSLN has not been met so far.